1. Field of the Invention
The present invention relates to a motorcycle frames, more particularly to a motorcycle frame having tubes extending away from a steering head tube in a three-dimensional trellis composite assembly, the assembly featuring frame main tubes interconnected by frame struts, and upper and lower frame main tubes oriented paired along at least one portion of their longitudinal extent substantially parallel to each other. The invention relates in addition to a motorcycle having a frame so described.
2. Background Art
A motorcycle frame must always satisfy two prime requirements, namely, for one thing, to take the weight of biker, co-biker, engine and transmission and other fitted components, for another, to ensure with other components of the chassis that the motorcycle affords good handling. Handling here is understood to be the response of the motorcycle as experienced by the biker, which is substantially influenced by the stiffness of the frame. Thus, changes in the stiffness of the motorcycle frame can change the handling of the motorcycle just as much as, for example, a significant change in the power of the engine or weight of the motorcycle.
Frame stiffness is always experienced by the biker when the motorcycle frame experiences a torsional moment. A torsional moment tends to twist the frame, i.e. instilling a twist between a steering head tube or handlebar header tube of the motorcycle frame and a swinging fork pivot bearing of the motorcycle frame, i.e. the location of the motorcycle frame at which the swinging fork responsible for rear wheel compliance introduces forces into the motorcycle frame.
Such a torsional moment acting on the motorcycle frame occurs, for example, when the motorcycle is cornering and the biker simultaneously decelerates the motorcycle. This deceleration is usually caused by actuating of the front wheel brake, resulting in a significant change in the distribution of the wheel loading of the motorcycle as compared to straight-on level travel. Once the biker has negotiated the bend with his motorcycle, the distribution of the wheel loading again changes, because the biker accelerates the motorcycle out of the bend which displaces the wheel loading mainly to the rear wheel. When this happens, the motorcycle is still slanted and due to the increasing speed the biker leans further to the inside of the bend at the same time as the wheel loading is further shifted in the direction of the rear wheel. When the motorcycle frame is engineered with relatively low stiffness, this results in elastic deformations of the frame detrimental to dynamic handling.
The biker has to compensate these elastic deformations by changing his response, for instance by changing the assumed line of travel, reducing engine power output, changing his seating posture relative to the yaw axis of the motorcycle, and so on. All of these actions result ultimately in delayed action of the motorcycle, as compared to a motorcycle having a stiffer motorcycle frame, to the detriment of dynamic handling. Subjectively too, low stiffness of the motorcycle frame is experienced by the biker as a disadvantage, as the motorcycle imparts a fuzzy feel in responding to the wanted action of the biker merely indirectly and delayed.
Thus, a motorcycle frame of low torsional rigidity experiences greater elastic deformations when loaded with a predefined torsional moment than a motorcycle frame having higher torsional rigidity. This is particularly significant for motorcycles designed for dynamic handling more often involved in changes in wheel load distribution and cornering than in normal travel. Increasing the torsional rigidity of the motorcycle frame can be achieved by increasing the dimensions of individual segments, for example frame main tubes or frame struts of the motorcycle frame, which is, however, contraproductive from the viewpoint of the increase in the mass of the motorcycle frame.
Motorcycle frames are available in a wealth of different embodiments. Thus, single loop frames already exist in which a single tube extends from the steering head tube and envelops the engine to fork in the region of the swinging fork pivot bearing. Likewise known are bridged frames which bypass the engine. In another known frame principle, the so-called double loop frame, two tubes extend from the steering head tube, passing the engine up to the swinging fork pivot bearing, and then back to the steering head tube. These return tubes are usually termed bracings. Also known in addition are sheet metal profile frames, consisting of two interwelded pressed steel half-shells. Other known types are so-called monocoque frames which, however, are less popular in motorcycle engineering. Lastly, also known are tubular trellis frames featuring a three-dimensional composite arrangements of frame tubes interconnected by frame struts.
In one such tubular trellis frame, the frame is configured similar to a trussed structure in which the engine as an integral component can contribute towards stiffening the frame and is thus configured as a co-supporting component. Likewise known are so-called central tube frames, featuring a central tube extending from the steering head tube to the region of the swinging fork pivot bearing and located above the engine and which can simultaneously be used to contain motorcycle consumables, for example as an oil tank.
A bridged frame featuring an integrated engine oil reservoir is known for example from German patent DE 101 35 931 C2.
A tubular trellis frame as described above is known, for example, from Japanese document JP-08216960 A. This frame has a steering head tube from which upper and lower frame main tubes extend, paired so that the aperture angle between the two frame main tubes exceeds 90 degrees in the direction of the longitudinal extension, the frame main tubes being interconnected by frame struts.
Known from Japanese document JP-09095284 is a tubular trellis frame featuring a steering head tube from which upper and lower frame main tubes extend, the upper and lower frame main tubes being interconnected by frame struts.
Known from Japanese document JP-011067789 A is a central tube frame, the central tube of which has a rectangular cross-section and extends from a steering head tube and featuring triangular links to which the engine of the motorcycle can be secured.
Suggested by U.S. Pat. No. 5,845,728 is a frame strut for a motorcycle, featuring a curved central tube extending from the steering head tube to the swinging fork pivot bearing. Extending away from a triangular composite assembly between the steering head tube of this frame are side links to which the engine can be secured.
A further motorcycle frame is known which features a steering head tube from which tubes in a three-dimensional lattice composite assembly extend in the form of frame main tubes interconnected by frame struts. The frame main tubes are upper and lower frame main tubes running essentially parallel along a portion of their longitudinally extent from the steering head tube. The motorcycle featuring this motorcycle frame finds application both on the road as a long-distance enduro and off the road. This known lightweight motorcycle frame features a high torsional rigidity but is characterized by being engineered as a tubular trellis frame with a plurality of tubes which need to be interwelded and thus complicating fabrication.
Against the foregoing backround, the apparatus of the present disclosure has the object of sophisticating the known motorcycle frame so that, although the total number of tubes joined into a trellis composite arrangement is reduced, improved strength performance is achieved without adding to the mass of the motorcycle frame.